Apparatus for producing a molten seal in a continuous casting furnace

ABSTRACT

A seal for a continuous casting furnace having a melting chamber with a mold therein for producing a metal cast includes a passage between the melting chamber and external atmosphere. As the cast moves through the passage, the cast outer surface and the passage inner surface define therebetween a reservoir for containing liquid glass or other molten material to prevent the external atmosphere from entering the melting chamber. Particulate material fed into the reservoir is melted by heat from the cast to form the molten material. The molten material coats the cast as it moves through the passage and solidifies to form a coating to protect the hot cast from reacting with the external atmosphere. Preferably, the mold has an inner surface with a cross-sectional shape to define a cross-sectional shape of the cast outer surface whereby these cross-sectional shapes are substantially the same as a cross-sectional shape of the passage inner surface.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/989,563, filed on Nov. 16, 2004; the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates generally to the continuous casting of metals.More particularly, the invention relates to the protection ofreactionary metals from reacting with the atmosphere when molten or atelevated temperatures. Specifically, the invention relates to using amolten material such as liquid glass to form a barrier to prevent theatmosphere from entering the melting chamber of a continuous castingfurnace and to coat a metal cast formed from such metals to protect themetal cast from the atmosphere.

2. Background Information

Hearth melting processes, Electron Beam Cold Hearth Refining (EBCHR) andPlasma Arc Cold Hearth Refining (PACHR), were originally developed toimprove the quality of titanium alloys used for jet engine rotatingcomponents. Quality improvements in the field are primarily related tothe removal of detrimental particles such as high density inclusions(HDI) and hard alpha particles. Recent applications for both EBCHR andPACHR are more focused on cost reduction considerations. Some ways toeffect cost reduction are increasing the flexible use of various formsof input materials, creating a single-step melting process (conventionalmelting of titanium, for instance, requires two or three melting steps)and facilitating higher product yield.

Titanium and other metals are highly reactive and therefore must bemelted in a vacuum or in an inert atmosphere. In electron beam coldhearth refining (EBCHR), a high vacuum is maintained in the furnacemelting and casting chambers in order to allow the electron beam guns tooperate. In plasma arc cold hearth refining (PACHR), the plasma arctorches use an inert gas such as helium or argon (typically helium) toproduce plasma and therefore the atmosphere in the furnace consistsprimarily of a partial or positive pressure of the gas used by theplasma torches. In either case, contamination of the furnace chamberwith oxygen or nitrogen, which react with molten titanium, may causehard alpha defects in the cast titanium.

In order to permit extraction of the cast from the furnace with minimalinterruption to the casting process and no contamination of the meltingchamber with oxygen and nitrogen or other gases, current furnacesutilize a withdrawal chamber. During the casting process the lengtheningcast moves out of the bottom of the mold through an isolation gate valveand into the withdrawal chamber. When the desired or maximum cast lengthis reached it is completely withdrawn out of the mold through the gatevalve and into the withdrawal chamber. Then, the gate valve is closed toisolate the withdrawal chamber from the furnace melt chamber, thewithdrawal chamber is moved from under the furnace and the cast isremoved.

Although functional, such furnaces have several limitations. First, themaximum cast length is limited to the length of the withdrawal chamber.In addition, casting must be stopped during the process of removing acast from the furnace. Thus, such furnaces allow continuous meltingoperations but do not allow continuous casting. Furthermore, the top ofthe cast will normally contain shrinkage cavities (pipe) that form whenthe cast cools. Controlled cooling of the cast top, known as a “hottop”, can reduce these cavities, but the hot top is a time-consumingprocess which reduces productivity. The top portion of the castcontaining shrinkage or pipe cavities is unusable material which thusleads to a yield loss. Moreover, there is an additional yield loss dueto the dovetail at the bottom of the cast that attaches to thewithdrawal ram.

The present invention eliminates or substantially reduces these problemswith a sealing apparatus which permits continuous casting of thetitanium, superalloys, refractory metals, and other reactive metalswhereby the cast in the form of an ingot, bar, slab or the like can movefrom the interior of a continuous casting furnace to the exteriorwithout allowing the introduction of air or other external atmosphereinto the furnace chamber.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a casting furnace for manufacturing ametal cast, the furnace comprising: an interior chamber having asidewall; a passage wall having an inner periphery which defines apassage extending through the sidewall of the interior chamber forcommunicating with the interior chamber and with atmosphere external tothe interior chamber; a circumferential space within the passage; ametal cast pathway extending from the interior chamber through thepassage and adapted for moving the metal cast from the interior chamberto the external atmosphere; a source of solid particulate coatingmaterial; a heat source for melting the particulate coating material toform molten coating material within the circumferential space; and adispenser for dispensing the solid particulate coating material in asolid state from the source directly into the circumferential spaceadjacent the pathway.

The present invention also provides a casting furnace for manufacturinga metal cast, the furnace comprising: an interior chamber having asidewall; a passage wall having an inner periphery which defines apassage extending through the sidewall of the interior chamber forcommunicating with the interior chamber and with atmosphere external tothe interior chamber; a metal cast pathway extending from the interiorchamber through the passage and adapted for moving the metal cast fromthe interior chamber to the external atmosphere; a molten bath boundingthe pathway along at least a portion of the passage and adapted toprevent the external atmosphere from entering the interior chamber; asource of particulate coating material; a dispenser for dispensing theparticulate coating material in a solid state from the source toadjacent the molten bath; and a heat source adjacent the molten bath formelting the particulate coating material to form molten coating materialfor the molten bath.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view of the seal of the present invention in usewith a continuous casting furnace.

FIG. 2 is similar to FIG. 1 and shows an initial stage of forming aningot with molten material flowing from the melting/refining hearth intothe mold and being heated by heat sources over each of the hearth andmold.

FIG. 3 is similar to FIG. 2 and shows a further stage of formation ofthe ingot as the ingot is lowered on a lift and into the seal area.

FIG. 4 is similar to FIG. 3 and shows a further stage of formation ofthe ingot and formation of the glass coating on the ingot.

FIG. 5 is an enlarged, view of the encircled portion of FIG. 4 and showsparticulate glass entering the liquid glass reservoir and the formationof the glass coating.

FIG. 6 is a sectional view of the ingot after being removed from themelting chamber of the furnace showing the glass coating on the outersurface of the ingot.

FIG. 7 is a sectional view taken on line 7-7 of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The seal of the present invention is indicated generally at 10 in FIGS.1-5 in use with a continuous casting furnace 12. Furnace 12 includes achamber wall 14 which encloses a melting chamber 16 within which seal 10is disposed. Within melting chamber 16, furnace 12 further includes amelting/refining hearth 18 in fluid communication with a mold 20 havinga substantially cylindrical sidewall 22 with a substantially cylindricalinner surface 24 defining a mold cavity 26 therewithin. Heat sources 28and 30 are disposed respectively above melting/refining hearth 18 andmold 20 for heating and melting reactionary metals such as titanium andsuperalloys. Heat sources 28 and 30 are preferably plasma torchesalthough other suitable heat sources such as induction and resistanceheaters may be used.

Furnace 12 further includes a lift or withdrawal ram 32 for lowering ametal cast 34 (FIG. 2-4). Any suitable withdrawal device may be used.Metal cast 34 may be in any suitable form, such as a round ingot,rectangular slab or the like. Ram 32 includes an elongated arm 36 with amold support 38 in the form of a substantially cylindrical plate seatedatop of arm 36. Mold support 38 has a substantially cylindrical outersurface 40 which is disposed closely adjacent inner surface 24 of mold20 as ram 32 moves in a vertical direction. During operation, meltingchamber 16 contains an atmosphere 42 which is non-reactive with reactivemetals such as titanium and superalloys which may be melted in furnace12. Inert gases may be used to form non-reactive atmosphere 42,particularly when using plasma torches, with which helium or argon areoften used, most typically the former. Outside of chamber wall 14 is anatmosphere 44 which is reactive with the reactionary metals when in aheated state.

Seal 10 is configured to prevent reactive atmosphere 44 from enteringmelting chamber 16 during the continuous casting of reactionary metalssuch as titanium and superalloys. Seal 10 is also configured to protectthe heated metal cast 34 when it enters reactive atmosphere 44. Seal 10includes a passage wall or port wall 46 having a substantiallycylindrical inner surface 47 defining passage 48 therewithin which hasan entrance opening 50 and an exit opening 52. Port wall 46 includes aninwardly extending annular flange 54 having an inner surface orcircumference 56. Inner surface 47 of port wall 46 adjacent entranceopening 50 defines an enlarged or wider section 58 of passage 48 whileflange 54 creates a narrowed section 60 of passage 48. Below annularflange 54, inner surface 47 of port wall 46 defines an enlarged exitsection 61 of passage 48.

As later explained, a reservoir 62 for a molten material such as liquidglass is formed during operation of furnace 12 in enlarged section 58 ofpassage 48. A source 64 of particulate glass or other suitable meltablematerial such as fused salt or slags is in communication with a feedmechanism 66 which is in communication with reservoir 62. Seal 10 mayalso include a heat source 68 which may include an induction coil, aresistance heater or other suitable source of heat. In addition,insulating material 70 may be placed around seal 10 to help maintain theseal temperature.

The operation of furnace 12 and seal 10 is now described with referenceto FIGS. 2-5. FIG. 2 shows heat source 28 being operated to meltreactionary metal 72 within melting/refining hearth 18. Molten metal 72flows as indicated by Arrow A into mold cavity 26 of mold 20 and isinitially kept in a molten state by operation of heat source 30.

FIG. 3 shows ram 32 being withdrawn downwardly as indicated by Arrow Bas additional molten metal 72 flows from hearth 18 into mold 20. Anupper portion 73 of metal 72 is kept molten by heat source 30 whilelower portions 75 of metal 72 begins to cool to form the initialportions of cast 34. Water-cooled wall 22 of mold 20 facilitatessolidification of metal 72 to form cast 34 as ram 32 is withdrawndownwardly. At about the time that cast 34 enters narrowed section 60(FIG. 2) of passage 48, particulate glass 74 is fed from source 64 viafeed mechanism 66 into reservoir 62. While cast 34 has cooledsufficiently to solidify in part, it is typically sufficiently hot tomelt particulate glass 74 to form liquid glass 76 within reservoir 62which is bounded by an outer surface 79 of cast 34 and inner surface 47of port wall 46. If needed, heat source 68 may be operated to provideadditional heat through port wall 46 to help melt particulate glass 74to ensure a sufficient source of liquid glass 76 and/or help keep liquidglass in a molten state. Liquid glass 76 fills the space withinreservoir 62 and narrowed portion 60 to create a barrier which preventsexternal reactive atmosphere 44 from entering melting chamber 16 andreacting with molten metal 72. Annular flange 54 bounds the lower end ofreservoir 62 and reduces the gap or clearance between outer surface 79of cast 34 and inner surface 47 of port wall 46. The narrowing ofpassage 48 by flange 54 allows liquid glass 76 to pool within reservoir62 (FIG. 2). The pool of liquid glass 76 in reservoir 62 extends aroundmetal cast 34 in contact with outer surface 79 thereof to form anannular pool which is substantially cylindrical within passage 48. Thepool of liquid glass 76 thus forms a liquid seal. After formation ofthis seal, a bottom door (not shown) which had been separatingnon-reactive atmosphere 42 from reactive atmosphere 44 may be opened toallow withdrawal of cast 34 from chamber 16.

As cast 34 continues to move downwardly as indicated in FIGS. 4-5,liquid glass 76 coats outer surface 79 of cast 34 as it passes throughreservoir 62 and narrowed section 60 of passage 48. Narrowed section 60reduces the thickness of or thins the layer of liquid glass 76 adjacentouter surface 79 of cast 34 to control the thickness of the layer ofglass which exits passage 48 with cast 34. Liquid glass 76 then coolssufficiently to solidify as a solid glass coating 78 on outer surface 79of cast 34. Glass coating 78 in the liquid and solid states provides aprotective barrier to prevent reactive metal 72 forming cast 34 fromreacting with reactive atmosphere 44 while cast 34 is still heated to asufficient temperature to permit such a reaction. Coating 78 alsoprovides an oxidation barrier at lower temperatures.

FIG. 5 more clearly shows particulate glass 74 traveling through feedmechanism 66 as indicated by Arrow C and into enlarged section 58 ofpassage 48 and into reservoir 62 where particulate glass 74 is melted toform liquid glass 76. FIG. 5 also shows the formation of the liquidglass coating in narrowed section 60 of passage 48 as cast 34 movesdownwardly. FIG. 5 also shows an open space between glass coating 78 andport wall 46 within enlarged exit section 61 of passage 48 as cast 34with coating 78 move through section 61.

Once cast 34 has exited furnace 12 to a sufficient degree, a portion ofcast 34 may be cut off to form an ingot 80 of any desired length, asshown in FIG. 6. As seen in FIGS. 6 and 7, solid glass coating 78extends along the entire circumference of ingot 80.

Thus, seal 10 provides a mechanism for preventing the entry of reactiveatmosphere 44 into melting chamber 16 and also protects cast 34 in theform of an ingot, bar, slab or the like from reactive atmosphere 44while cast 34 is still heated to a temperature where it is stillreactive with atmosphere 44. As previously noted, inner surface 24 ofmold 20 is substantially cylindrical in order to produce a substantiallycylindrical cast 34. Inner surface 47 of port wall 46 is likewisesubstantially cylindrical in order to create sufficient space forreservoir 62 and space between cast 34 and inner surface 56 of flange 54to create the seal and also provide a coating of appropriate thicknesson cast 34 as it passes downwardly. Liquid glass 76 is nonetheless ableto create a seal with a wide variety of transverse cross-sectionalshapes other than cylindrical. The transverse cross-sectional shapes ofthe inner surface of the mold and the outer surface of the cast arepreferably substantially the same as the transverse cross-sectionalshape of the inner surface of the port wall, particularly the innersurface of the inwardly extending annular flange in order that the spacebetween the cast and the flange is sufficiently small to allow liquidglass to form in the reservoir and sufficiently enlarged to provide aglass coating thick enough to prevent reaction between the hot cast andthe reactive atmosphere outside of the furnace. To form a metal castsuitably sized to move through the passage, the transversecross-sectional shape of the inner surface of the mold is smaller thanthat of the inner surface of the port wall.

Additional changes may be made to seal 10 and furnace 12 which are stillwithin the scope of the present invention. For example, furnace 12 mayconsist of more than a melting chamber such that material 72 is meltedin one chamber and transferred to a separate chamber wherein acontinuous casting mold is disposed and from which the passage to theexternal atmosphere is disposed. In addition, passage 48 may beshortened to eliminate or substantially eliminate enlarged exit section61 thereof. Also, a reservoir for containing the molten glass or othermaterial may be formed externally to passage 48 and be in fluidcommunication therewith whereby molten material is allowed to flow intoa passage similar to passage 48 in order to create the seal to preventexternal atmosphere from entering the furnace and to coat the exteriorsurface of the metal cast as it passes through the passage. In such acase, a feed mechanism would be in communication with this alternatereservoir to allow the solid material to enter the reservoir to bemelted therein. Thus, an alternate reservoir may be provided as amelting location for the solid material. However, reservoir 62 of seal10 is simpler and makes it easier to melt the material using the heat ofthe metal cast as it passes through the passage.

The seal of the present invention provides increased productivitybecause a length of the cast can be cut off outside the furnace whilethe casting process continues uninterrupted. In addition, yield isimproved because the portion of each cast that is exposed when cut doesnot contain shrinkage or pipe cavities and the bottom of the cast doesnot have a dovetail. In addition, because the furnace is free of awithdrawal chamber, the length of the cast is not limited by such achamber and thus the cast can have any length that is feasible toproduce. Further, by using an appropriate type of glass, the glasscoating on the cast may provide lubrication for subsequent extrusion ofthe cast. Also the glass coating on the cast may provide a barrier whensubsequently heating the cast prior to forging to prevent reaction ofthe cast with oxygen or other atmosphere.

While the preferred embodiment of the seal of the present invention hasbeen described in use with glass particulate matter to form a glasscoating, other materials may be used to form the seal and glass coating,such as fused salt or slags for instance.

The present apparatus and process is particularly useful for highlyreactive metals such as titanium which is very reactive with atmosphereoutside the melting chamber when the reactionary metal is in a moltenstate. However, the process is suitable for any class of metals, e.g.superalloys, wherein a barrier is needed to keep the external atmosphereout of the melting chamber to prevent exposure of the molten metal tothe external atmosphere.

In the foregoing description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued.

Moreover, the description and illustration of the invention is anexample and the invention is not limited to the exact details shown ordescribed.

1. A casting furnace for manufacturing a metal cast, the furnacecomprising: an interior chamber having a sidewall; a passage wall havingan inner periphery which defines a passage extending through thesidewall of the interior chamber for communicating with the interiorchamber and with atmosphere external to the interior chamber; acircumferential space within the passage; a metal cast pathway extendingfrom the interior chamber through the passage and adapted for moving themetal cast from the interior chamber to the external atmosphere; asource of solid particulate coating material; a heat source for meltingthe particulate coating material to form molten coating material withinthe circumferential space; and a dispenser for dispensing the solidparticulate coating material in a solid state from the source directlyinto the circumferential space adjacent the pathway.
 2. The furnace ofclaim 1 in combination with the metal cast; and wherein the heat sourcecomprises heat radiating from the metal cast.
 3. The combination ofclaim 2 wherein the heat radiating from the metal cast is sufficient formelting the particulate coating material.
 4. The furnace of claim 1wherein the furnace is free of a melting chamber for melting the solidcoating material at a location external to the interior chamber.
 5. Thefurnace of claim 4 wherein the circumferential space is the onlylocation of the furnace for melting the particulate material.
 6. Thefurnace of claim 1 wherein the passage has a transverse cross-sectionalshape adapted to be substantially the same as and larger than atransverse cross-sectional shape of the metal cast.
 7. The furnace ofclaim 1 further comprising a continuous casting mold in the interiorchamber; an inner surface on the mold defining a transversecross-sectional shape adapted to define a transverse cross-sectionalshape of the metal cast; and a section of the inner periphery of thepassage wall defining a narrowest portion of the passage having atransverse cross-sectional shape substantially the same as and largerthan the transverse cross-sectional shape defined by the inner surfaceof the mold.
 8. The furnace of claim 1 in combination with the metalcast; and further comprising a molten bath at least a portion of whichis disposed in the circumferential space; and wherein the metal cast hasan outer periphery; and the circumferential space is defined between theouter periphery of the metal cast and the inner periphery of the passagewall.
 9. The combination of claim 8 wherein the molten bath is incontact with the outer periphery of the metal cast to form a protectivebarrier thereon as the metal cast moves from the interior chamber to theexternal atmosphere.
 10. The combination of claim 9 wherein the passagewall comprises an inwardly projecting annular flange which defines anarrower portion of the passage; the passage wall above the flangedefines a wider portion of the passage; and the inner periphery of theflange is spaced from and adjacent the outer periphery of the metal castas it moves through the passage to define a thickness of the protectivebarrier.
 11. A casting furnace for manufacturing a metal cast, thefurnace comprising: an interior chamber having a sidewall; a passagewall having an inner periphery which defines a passage extending throughthe sidewall of the interior chamber for communicating with the interiorchamber and with atmosphere external to the interior chamber; a metalcast pathway extending from the interior chamber through the passage andadapted for moving the metal cast from the interior chamber to theexternal atmosphere; a molten bath bounding the pathway along at least aportion of the passage and adapted to prevent the external atmospherefrom entering the interior chamber; a source of particulate coatingmaterial; a dispenser for dispensing the particulate coating material ina solid state from the source to adjacent the molten bath; and a heatsource adjacent the molten bath for melting the particulate coatingmaterial to form molten coating material for the molten bath.
 12. Thefurnace of claim 11 further comprising an exit end on the dispenseradjacent the metal cast pathway and above the molten bath.
 13. Thefurnace of claim 12 in combination with the metal cast; and furthercomprising an outer periphery on the metal cast; and wherein the exitend is adjacent the outer periphery of the metal cast when movingthrough the passage via the pathway.
 14. The furnace of claim 11 furthercomprising an exit end on the dispenser adjacent the inner periphery ofthe passage wall.
 15. The furnace of claim 11 further comprising an exitend on the dispenser adjacent the passage wall and above the moltenbath.
 16. The furnace of claim 15 wherein the passage wall has an upperend; and the exit end of the dispenser is adjacent the upper end of thepassage wall.
 17. The furnace of claim 11 further comprising acontinuous casting mold in the interior chamber adapted for producingthe metal cast; and an exit end on the dispenser below the mold.
 18. Thefurnace of claim 11 wherein the furnace is free of a melting chamber formelting the solid coating material at a location external to theinterior chamber.
 19. The furnace of claim 11 in combination with themetal cast; and wherein the heat source comprises heat radiating fromthe metal cast.
 20. The combination of claim 19 wherein the heatradiating from the metal cast is sufficient for melting the particulatecoating material.